Controlling flow in a medical injection system

ABSTRACT

A valve apparatus for a medical injection system includes a pinching member and at least one spring-loaded anvil. A tubing line of the injection system may be positioned between the pinching member and the anvil, such that when the pinching member is moved into a pinching position adjacent to the anvil, for example, by rotation of a shaft to which the member is coupled, the pinching member compresses the tubing line against the spring-loaded anvil. The pinching member is preferably rotatable about an auxiliary axis, which is eccentric, or offset from a central axis of the shaft. A spring member of the spring-loaded anvil is preferably pre-loaded. In certain applications, the pinching member, when moved into the pinching position, applies a pinching force of greater than approximately 45 pounds, for example, to prevent flow through the tubing line at an injection pressure of up to approximately 1200 psi.

TECHNICAL FIELD

The present disclosure pertains to medical injection systems and moreparticularly to apparatus and methods for controlling flow therein.

BACKGROUND

FIG. 1A is a perspective view of an exemplary medical injection system100 (the ACIST CV_(i)® system) for delivering a contrast agent into apatient's vascular system for medical imaging. FIG. 1A illustrates afirst fluid reservoir 132 for supplying a syringe-type positivedisplacement pump of a pressurizing unit 130, via a fill tubing line27-F, and an injection tubing line 27-I coupled to unit 130 forinjection of, for example, a radiopaque contrast agent, into a patient'svascular system via an inserted catheter (not shown), for example,coupled to a patient tubing line 122 at a connector 120 thereof. FIG. 1Afurther illustrates a second fluid reservoir 138 from which a diluent,such as saline, is drawn by a peristaltic pump 106 through yet anothertubing line 128 that feeds into tubing line 122. A manifold valve 124and associated sensor 114 control the flow of fluids into tubing line122, from pressurizing unit 130 and from tubing line 128.

Although not shown in FIG. 1, the syringe-type positive displacementpump of unit 130 includes a fill port and an injection port to whichtubing lines 27-F and 27-I, respectively are coupled; a check valve (notshown) in line 27-F and valve 124 in line 27-I are employed to controlflow through tubing lines 27-F and 27-I. For example, when the pump ofunit 130 is activated to draw in fluid from reservoir 132, flow fromtubing lines 122 and 128 through injection tubing line 27-I is blockedby valve 124; and, after the pump is filled, when the pump is activatedto pressurize the fluid therein, valve 124 is opened to allow flow ofthe pressurized fluid through line 27-I and into line 122, while flowthrough fill tubing line 27-F is blocked by the aforementioned checkvalve. A variety of alternative valve mechanisms for controlling theflow through tubing lines of medical injection systems, such as tubinglines 27-F and 27-I of injection system 100, are known in the art. Forexample, a suitable pinch valve apparatus is described incommonly-assigned U.S. Pat. No. 8,152,780. Yet, there is still a needfor improved valve apparatus that simplify and increase the efficiencyof valve operation to control flow in medical injection systems.

SUMMARY

Apparatus and methods of the present invention are directed towardcontrolling flow through one or more tubing lines of a medical injectionsystem. According to some methods, which may be employed by an injectionsystem that includes fill and injection tubing lines coupled a pump, thetwo tubing lines are positioned in a valve apparatus such that a firstof the two lines is located between a pinching member of the apparatusand a spring-loaded anvil of the apparatus, and a second of the twolines is located between the pinching member and a second spring-loadedanvil of the apparatus; subsequently, the pinching member is moved froma first position, at which the pinching member compresses the firsttubing line against the first spring-loaded anvil, to a second position,at which the pinching member compresses the second tubing line againstthe second spring-loaded anvil, and vice versa. When the pinching membercompresses the first tubing line, flow therethrough is blocked while thepump draws fluid in through the second tubing line; and, when thepinching member compresses the second tubing line, flow therethrough isblocked while the pump injects the fluid out through the first tubingline, for example, at an injection pressure of up to approximately 1200psi, according to some embodiments and methods. In alternative injectionsystems, a single tubing line may be positioned in a similar valveassembly that includes only one spring-loaded anvil in conjunction withthe pinching member.

According to some preferred embodiments, the pinching member is coupledto a rotatable shaft, for example, driven by a motor that moves thepinching member about a central axis of the shaft between the first andsecond positions, and through a neutral position therebetween (where thepinching member may be located when the tubing lines are initiallypositioned in the valve apparatus). Furthermore, the pinching member ispreferably rotatable about an auxiliary axis, which is eccentric, oroffset from the central axis of the shaft, so that pinching member rollsinto and out of contact with the tubing lines when moved back and forthbetween the first and second positions. A spring member of each of thespring-loaded anvils may be in the form of an elongate flexure that hasa fixed end and a floating end, to which an anvil block, on which thecorresponding anvil is formed, is attached. According to some preferredmethods and embodiments, each spring-member is pre-loaded, for example,prior to moving the pinching member to compress one of the tubing linesin the valve apparatus. Furthermore, a minimum gap between eachpre-loaded spring-loaded anvil and the pinching member in one or both ofthe first and second positions is preferably established for anapproximate 20% squeeze reduction of the wall thickness of thecorresponding tubing line minus a maximum in-service deflection of thecorresponding pre-loaded spring member, which in-service deflection ispreferably established, for a given spring constant of the pre-loadedspring member, to provide a pinching force of greater than approximately45 pounds, with a variability within approximately 15% of nominal, overthe range of in-service deflection.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular methods andembodiments of the present disclosure and, therefore, do not limit thescope of the invention. The drawings are not to scale (unless so stated)and are intended for use in conjunction with the explanations in thefollowing detailed description. Methods and embodiments will hereinafterbe described in conjunction with the appended drawings, wherein likenumerals denote like elements, and:

FIGS. 1A-B are perspective views of at least portions of exemplarymedical injection systems that may employ embodiments of the presentinvention;

FIG. 2A is a plan view of fill and injection tubing lines that extendfrom a positive displacement pump and through a valve apparatus,according to some embodiments and methods of the present invention;

FIG. 2B is an enlarged plan view of the apparatus of FIG. 2A, accordingto some embodiments;

FIG. 3 is a perspective view of the valve apparatus, according to someembodiments;

FIG. 4A is a longitudinal cross-section view through section line 4-4 ofFIG. 2B, according to some embodiments;

FIG. 4B is a schematic representation of an exemplary valve apparatus inwhich schematic spring elements are employed;

FIG. 5A is a chart defining torque output of a suitable stepping motor,according to some embodiments; and

FIG. 5B is another schematic for reference in conjunction withdescription of the exemplary valve apparatus.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description providespractical illustrations for implementing exemplary methods andembodiments. Examples of constructions, materials and dimensions areprovided for selected elements, and all other elements employ that whichis known to those of skill in the field of the invention. Those skilledin the art will recognize that many of the examples provided havesuitable alternatives that can be utilized.

FIG. 2A is a plan view of a portion of fill tubing line 27-F and aportion of injection tubing line 27-I, both of which extend from apositive displacement pump 230 and through a valve apparatus 23,according to some embodiments and methods of the present invention. Filltubing line 27-F is shown coupled to a fill port 26-F of pump 230 andinjection line 27-I to an injection port 26-I of pump 230. Withreference back to FIG. 1A, it may be appreciated that pump 230 may beemployed by, and integrated into pressurizing unit 130 of system 100,and valve apparatus 23 may be employed in system 100, to take over forthe aforementioned check valve and manifold valve 124 by controllingflow through lines 27-F and 27-I. FIG. 2A illustrates valve apparatus 23including a pinching member 233, a first spring-loaded anvil 271, and asecond spring-loaded anvil 272; injection tubing line 27-I is shownextending between first anvil 271 and pinching member 233, and filltubing line 27-F between second anvil 272 and pinching member 233. Eachof tubing lines 27-F, 27-I may be formed from a nylon reinforcedpolyurethane or a flexible PVC material, both of which are known tothose skilled in the art. In FIG. 2A, pinching member 233 compressesfill tubing line 27-F against spring-loaded anvil 272 to block a flow offluid therethrough from pump 230, when a plunger 32 of pump 230 movesper arrow I to pressurize and inject the fluid out through injectiontubing line 27-I. FIG. 2A further illustrates pinching member 233 beingcoupled to a shaft 232, which is preferably rotatable about a centralaxis 203 thereof, for example, back and forth according to double-headedarrow a of FIG. 2B, to move member 233 between first and secondpositions 1, 2.

FIG. 2B is an enlarged plan view of valve apparatus 23, wherein dashedlines indicate first position 1 of pinching member 233, prior tomovement to second position 2, which is the same as that illustrated inFIG. 2A. FIGS. 2A-B illustrate pinching member 233 being centered on anauxiliary axis 213, which is eccentric, or offset from central axis 203.With further reference to FIG. 2B, a rotation of shaft 232, to movepinching member 233 between first position 1 and second position 2,through a neutral position N, is illustrated by three locations ofauxiliary axis 213. It may be appreciated that, according to preferredmethods of the present invention, pinching member 233 is initiallylocated in neutral position N when pump 230 and tubing lines 27-F, 27-Iare loaded into an injection system, for example, to increase the easeof positioning lines 27-F and 27-I between pinching member 233 and thecorresponding spring-loaded anvil 271, 272 within valve apparatus 23.Then, once pump 230 and lines 27-F, 27-I are loaded, pinching member 233is moved into first position 1 to block flow from line 27-I, beforeplunger 32 of pump 230 is moved, per arrow F (FIG. 2A), to draw fluid inthrough tubing line 27-F. After plunger 32 draws a predetermined volumeof fluid into pump 230, pinching member 233 is moved from first position1 to second position 2, as illustrated in FIG. 2A, to block flow throughtubing line 27-F while pump 230 expels the fluid through line 27-I, forexample, at an injection pressure of up to approximately 1200 psi.

FIG. 3 is a perspective view of valve apparatus 23, according to someembodiments. FIG. 3 illustrates shaft 232 supported in a structure 305,for example, by a ball bearing assembly 422, which may be seen in thecross-section view of FIG. 4A. FIG. 4A is a longitudinal cross-sectionview through section line 4-4 of FIG. 2B, according to some embodiments.FIG. 4A further illustrates shaft 232 being coupled to a shaft 315 of amotor 335, for example, a stepping motor (i.e. Item #PK235PDA describedat http://catalog.orientalmotor.com), which is contained in a fixedhousing of valve apparatus 23. With reference back to FIG. 1A, and asalluded to above, valve apparatus 23 may be employed by system 100, forexample, by mounting apparatus 23 in the general vicinity indicated byreference letter P so that motor 335 sits to the rear of a generallyvertical plane V, in which fill and injection ports 26-F, 26-I of pump230 lie, and shaft 232 extends toward tubing lines 27-F, 27-I; thus,lines 27-F, 27-I may be positioned in valve apparatus 23 as illustratedin FIG. 2A. Furthermore, with reference to FIG. 1B, an injection system200, which has an alternative configuration, may employ a pair of valveapparatus 23. FIG. 1B illustrates system 200 including a pair of sleeves216A, 216B, each of which may house a pump like pump 230 (FIG. 2A), suchthat a set of tubing lines 27-F, 27-I, which are routed from each pumpwithin a corresponding compartment 218A, 218B, lie in a generallyhorizontal plane H. According to the illustrated embodiment, one of thetwo pumps may pump saline, for example, filled form a reservoir mountedon a fixture 202A, and another of the pumps may pump a contrast agent,for example, filled from a reservoir mounted on a fixture 202B; a guide220 is shown extending from compartments 218A, 218B for connecting thesaline and contrast injection lines to a patient line. With furtherreference to FIG. 1B, motor 335 of each valve apparatus 23 employed bysystem 200 may be mounted in the general vicinity indicated by referenceletter P, below plane H, so that shaft 232 of each extends toward thecorresponding set of tubing lines 27-F, 27-I; thus, each set of tubinglines may be positioned in the corresponding valve apparatus 23 asillustrated in FIG. 2A.

Motor 335 of valve apparatus 23, when actuated (i.e. eitheruser-actuated, or actuated in response to a trigger signal from a sensorcoupled to pump 230), drives shaft 232 with sufficient torque to forcepinching member 233, either into position 1, to compress tubing line27-I against spring-loaded anvil 271, or into position 2, to compresstubing line 27-F against spring-loaded anvil 272, and therebyeffectively block flow through lines 27-I and 27-F, in succession. Aswas generally described above, once tubing lines 27-I, 27-F arepositioned in valve assembly 23, motor 335 may be actuated to movepinching member 233 to first position 1, at which member 233 compressestubing line 27-I against anvil 271, while pump 230 draws in fluid from areservoir, for example, reservoir 132 of FIG. 1, through tubing line27-F; then, once pump 230 is filled, motor is actuated to move pinchingmember 233 to second position 2 in order to compress tubing line 27-Fwhile pump injects the fluid through tubing line 27-I. Over the courseof one or more imaging procedures, pump 230 may need to be filled asmany as approximately 5 times up to approximately 25 times; thuspinching member 233 is repeatedly moved between first and secondpositions 1, 2 enough times to replenish the volume of pump 230 andthereby support the required number of injections. According to somepreferred methods, motor 335 drives shaft back and forth through neutralposition N, approximately 180 degrees about central axis 203, to movepinching member 233, between first and second positions 1, 2;alternatively, motor 335 may drive shaft 232 360 degrees around centralaxis 203 to move pinching member 233 between first and second positions1, 2. The stepping motor preferably includes an encoder to monitor thesteps of the rotation of shaft 232 in order to keep track of, andconfirm the position of pinching member 233 during system operation.

FIG. 3 further illustrates each of anvils 271, 272 spring-loaded byvirtue of attachment to a corresponding spring member, each of which isin the form of an elongate flexure 370. FIG. 3 illustrates a first end301 of each flexure 370 attached to support structure 305, and each ofanvils 271, 272 being formed on a corresponding anvil block 257, whichis fastened to a floating second end 302 of the corresponding flexure370. Reference numeral 307 designates locations for exemplary fasteners,some of which may be seen in FIG. 4A. Each of anvils 271, 272 preferablyextends over a width w that is greater than or equal to an outerdiameter of each of tubing lines 27-F, 27-I, and each may have a radiusR-n of between approximately 0.06 inch (1.5 mm) and approximately 0.08inch (2 mm), for example, to effectively pinch tubing lines 27-I, 27-Fwithout damaging the walls thereof by applying undue stress. Anvilblocks 257 are preferably formed from stainless steel.

With further reference to FIGS. 2B and 4A, for a given wall thicknessand material properties of the tubes forming tubing lines 27-F, 27-I, aminimum gap g_(min) is established between pinching member 233 and eachof anvils 271, 272. (g_(min) is shown between second anvil 272 andmember 233 in second position 2.) When tubing lines, for example, lines27-I and 27-F, are positioned within valve apparatus 23, for example asillustrated in FIG. 2A, the spring loading provided by flexures 370establishes a relatively constant pinching pressure between each ofanvils 271, 272 and pinching member 233 in the first and secondpositions 1, 2, respectively, for example, across a standard tolerancerange wall thickness for the tubing forming each of tubing lines 27-I,27-F. Furthermore, the spring loading of anvils 271, 272 maintains therelatively constant pinching pressure if the stiffness of either tubingline 27-I, 27-F creeps/declines in response to multiple pinch cycles,for example, up to as many as approximately 25 cycles, which may takeplace over the course of an imaging procedure, or a day of multipleimaging procedures, as described above.

With reference back to FIG. 4A, according to some preferred methods andembodiments, flexures 370 are pre-loaded to establish a desired pinchingforce applied by pinching member 233, and to reduce an amplitude ofcyclic loading seen by each flexure 370 over the life of valve apparatus23, for example, corresponding to up to approximately 60,000 pinchcycles. FIG. 4A illustrates pre-load supports 417, each of which ispreferably formed in support structure 305; each support 417 is locatedadjacent anvil block 257 at floating second end 302 of the correspondingelongate flexure 370.

FIG. 4A further illustrates pinching member 233 supported by a needlebearing assembly 423, such that member 233 is rotatable around auxiliaryaxis 213. Such support is preferred to allow pinching member 233 to rollinto and out of contact with tubing lines 27-F, 27-I, therebyfacilitating the movement of pinching member into, and out from firstand second positions 1, 2 without displacing the corresponding tubingline 27-F, 27-I along a direction of its longitudinal axis, and/orwithout undue wear on tubing lines 27-F, 27-I.

EXAMPLE

According to an exemplary embodiment, each tubing line 27-I, 27-F isformed by a nylon-reinforced polyurethane tube having a nominal outerdiameter of approximately 0.188 inch (4.78 mm) and a nominal wallthickness t of approximately 0.05 inch (1.27 mm). Pinching member 233and each spring-loaded anvil 271, 272 are suitably dimensioned,supported and arranged in valve apparatus 23 so that member 233 and eachanvil 271, 272 apply a sufficient pinching force to each of theexemplary tubing lines 27-I, 27-F, when each tubing line is positionedin valve apparatus 23 (i.e. per FIG. 2A), and when member 233 is in thefirst and second positions 1, 2, respectively. The sufficient pinchingforce, which prevents flow through the exemplary tubing lines at amaximum injection pressure of approximately 1200 psi has been found tobe approximately 45 pounds, but, in order to assure a tubing failure(i.e. burst at approximately 1500 psi) prior to a cracking/leak throughthe pinching of fill tubing line 27-F, between pinching member 233 andspring-loaded anvil 272, at injection pressures exceeding the 1200 psi,a safety margin of 10 pounds brings the pinching force to approximately55 pounds for the exemplary embodiment. Thus, prevention of backflowthrough fill tubing line 27-F is assured during injections throughinjection tubing line 27-I. Furthermore, in the exemplary embodiment,the aforementioned exemplary stepping motor (Item #PK235PDA;http://catalog.orientalmotor.com), which operates according to thetorque curve shown in FIG. 5A, applies sufficient torque, via shafts 315and 232, to repeatedly move pinching member 233 from first position 1 tosecond position 2, and vice versa, without stalling, when theaforementioned tubes for each tubing line 27-I, 27-F are positioned invalve apparatus 23.

With reference to FIG. 4A, each exemplary elongate flexure 370 is formedfrom a fully hardened stainless steel strip, which has a spring constantof approximately 439 lb/in; and each flexure 370 extends between thecorresponding fixed end 301 and the corresponding anvil block 257, overa length L, which is approximately 1.42 inch. The minimum gap g_(min),which is between first anvil 271 and pinching member 233, when member233 is in first position 1 (FIG. 2B), and between second anvil 272 andpinching member 233, when member is in second position 2, as shown inFIG. 4A, is set to approximately 0.05 inch (1.27 mm) for the exemplaryembodiment. With reference to the schematic shown in FIG. 4B, thisminimum gap g_(min) is established according to a desired 20% squeezereduction of the wall thickness t of each of tubing lines 27-I, 27-F andaccording to a maximum in-service deflection δs of spring-loaded anvils271, 272, which is approximately 0.03 inch (0.76 mm). FIG. 4Billustrates a deflection of tubing lines 27-F, 27-I equal to the 20%reduction plus an inner diameter ID of each tubing line. FIG. 4B furtherillustrates a pre-load deflection δp, which, when established atapproximately 0.09 inch for each spring-loaded anvil 271, 272, forexample, by pre-load supports 417 abutting each exemplary flexure 370(FIG. 4A), assures that a radial force F_(R) (shown in the schematic ofFIG. 5B), applied to positioned tubing lines 27-I, 27-F by each ofspring-loaded anvils 271, 272, with pinching member 233 positioned inthe first and second positions 1, 2, respectively, is approximatelymaintained at the aforementioned 55 pound pinching force. It should benoted that FIG. 4B illustrates spring-loaded anvils 271, 272 and tubinglines 27-F, 27-I as schematic spring elements transitioning in responseto deflections imposed by pre-loading and by movement of pinching member233 from the above-described neutral position N and into one of theabove-described first and second positions 1, 2, wherein pinching member233 is at top or bottom dead center DC when the maximum in-servicedeflection δs is achieved. According to preferred embodiments, thespring constant of flexures 370, minimum gap g_(min) and pre-loaddeflection δp determine a maximum in-service deflection δs, for the 20%squeeze reduction, that limits a variation in the 55 pound pinchingforce, for example, to within approximately 15% of nominal, throughoutthe range of in-service deflection δs (i.e. from initial compression ofeach tubing line 27-F, 27-I to top dead center DC).

FIG. 5B is a schematic demonstrating how a diameter D of pinching member233 and an offset e, in conjunction with radial force F_(R) and a dragforce F_(D), dictate the torque necessary to move member 233 into firstand second positions 1, 2 (FIG. 2B). The aforementioned pre-loaddeflection δp, along with a maximum rolling friction coefficient μ ofapproximately 0.005, for needle bearing assembly 423 with respect to aperimeter of pinching member 233, helps to limit the drag force F_(D) onpinching member 233 as member 233 rolls into contact with each ofpositioned tubing lines 27-F, 27-I. Furthermore, diameter D of pinchingmember 233, which is set to approximately 1.1 inch (28 mm), and offset eof auxiliary axis 213 from central axis 203, which is set toapproximately 0.118 inch (3 mm), establish a maximum pressure angle α ofapproximately 12.4 degrees, which also contributes to limiting the dragforce F_(D). Equations for both the maximum pressure angle and the dragforce are shown in FIG. 5B, as is the equation governing the maximumtorque T required to move pinching member 233 into the first and secondpositions 1, 2. Thus, according to the exemplary embodiment, theaforementioned stepping motor, performing according to the torque curveshown in FIG. 5A, is able to repeatedly move pinching member 233 intothe first and second positions 1, 2, at which the aforementionedpinching force is applied to each tubing line 27-I, 27-F, respectively.Furthermore, the motor may drive shaft 232 at a speed to move pinchingmember 233 from neutral position N to either of the first and secondpositions 1, 2, within a time of approximately 250 milliseconds.Preferably, the motor moves pinching member 233 back and forth, through180 degrees, between the first and second positions 1, 2, as describedabove in conjunction with FIG. 2B; but this exemplary embodiment doesnot rule out 360 degree movement of pinching member 233.

Finally, it should be noted that embodiments of the disclosed valveapparatus may be employed to control flow only through injection lines,for example, in systems that do not require pump filling and theassociated fill tubing lines. In this context, the above-describedembodiments may operate to control flow through two injection lines,successively, by moving back and forth between the two positions 1, 2,or may operate to control flow in a single injection line, for example,by only moving between the neutral position N and the first position 1.

In the foregoing detailed description, the invention has been describedwith reference to specific embodiments. However, it may be appreciatedthat various modifications and changes can be made without departingfrom the scope of the invention as set forth in the appended claims.

We claim:
 1. A method for controlling flow in a medical injectionsystem, the system including a pump having an inlet port and an outletport, the outlet port being coupled to a first tubing line that isadapted to receive therethrough injections of fluid expelled from thepump, and the inlet port being coupled to a second tubing line thatextends from a fluid reservoir for filling the pump, and the methodcomprising: positioning the first tubing line between a pinching memberand a first spring-loaded anvil, and positioning the second tubing linebetween the pinching member and a second spring-loaded anvil; and movingthe pinching member from a first position, at which the pinching membercompresses the first tubing line against the first spring-loaded anvil,to a second position, at which the pinching member compresses the secondtubing line against the second spring-loaded anvil.
 2. The method ofclaim 1, further comprising activating the pump to expel fluid throughthe first tubing line at an injection pressure of up to approximately1200 psi after moving the pinching member; and wherein the pinchingmember in the second position compresses the second tubing line enoughto prevent backflow therethrough at the injection pressure.
 3. Themethod of claim 1, further comprising moving the pinching member from aneutral position to the first position, prior to moving the pinchingmember from the first position to the second position; wherein thepinching member is located at the neutral position when the first andsecond tubing lines are positioned, and the pinching member compressesneither of the first and second tubing lines when located at the neutralposition.
 4. The method of claim 1, wherein moving the pinching memberfrom the first position to the second position comprises actuating amotor to rotate a shaft to which the pinching member is coupled, afterthe pump has been filled with a predetermined volume of fluid from thereservoir through the second tubing line.
 5. The method of claim 1,wherein moving the pinching member comprises rotating a shaft to whichthe pinching member is coupled, and the pinching member moves around acentral axis of the rotating shaft and through a neutral positionbetween the first and second positions.
 6. The method of claim 5,wherein the pinching member is rotatable about an auxiliary axis that isoffset from the central axis of the shaft, such that the pinching memberrolls out of contact with the first tubing line and then into contactwith the second tubing line, when the pinching member is moved from thefirst position to the second position.
 7. The method of claim 1, furthercomprising pre-loading a spring member of each of the first and secondspring-loaded anvils prior to moving the pinching member from the firstposition to the second position.
 8. The method of claim 7, furthercomprising: establishing a minimum gap between each spring-loaded anviland the pinching member in the corresponding position for an approximate20% squeeze reduction of a wall thickness of the corresponding tubingline minus a maximum in-service deflection of each pre-loaded springmember; and wherein the maximum in-service deflection of each pre-loadedspring member provides a pinching force on each tubing line beingcompressed between the pinching member and the correspondingspring-loaded anvil of greater than approximately 45 pounds, thepinching force varying within approximately 15% of nominal over therange of the maximum in-service deflection.
 9. The method of claim 1,wherein moving the pinching member from the first position to the secondposition comprises actuating a motor to rotate a shaft to which thepinching member is coupled, after the pump has been filled with apredetermined volume of fluid from the reservoir through the secondtubing line; and further comprising: activating the pump to expel fluidthrough the first tubing line at an injection pressure of up toapproximately 1200 psi, after moving the pinching member to the secondposition; and moving the pinching member from the second position backto the first position, after the pump has expelled all or a portion ofthe predetermined volume of the fluid; wherein the pinching member inthe second position compresses the second tubing line enough to preventbackflow therethrough at the injection pressure.
 10. A valve apparatusfor controlling flow through a pair of tubing lines of a medicalinjection system, the apparatus comprising: a rotatable shaft; apinching member coupled to the rotatable shaft such that the pinchingmember moves around a central axis of the shaft when the shaft isrotated; a first anvil attached to a first spring member and located ona first side of the shaft; and a second anvil attached to a secondspring member and located on a second side of the shaft, the second sidebeing generally opposite the first side; wherein rotation of the shaftmoves the pinching member from a first position, adjacent to the firstanvil, to a second position, adjacent to the second anvil; and when thepinching member is in the first position, a minimum gap between thefirst anvil and the pinching member is less than twice a wall thicknessof one of the pair of tubing lines.
 11. The apparatus of claim 10,wherein, when the pinching member is in the second position, a minimumgap between the second anvil and the pinching member is less than twicea wall thickness of the other of the pair of tubing lines.
 12. Theapparatus of claim 10, wherein each of the first and second springmembers comprises an elongate flexure, each flexure having a fixed firstend and a floating second end, each second end having the correspondinganvil attached thereto.
 13. The apparatus of claim 12, furthercomprising a pair of pre-load supports, each pre-load support locatedadjacent a corresponding floating second end of the correspondingflexure for pre-loading thereof.
 14. The apparatus of claim 13, furthercomprising a fixed structure supporting the shaft; wherein the firstfixed end of each flexure is coupled to the structure and each pre-loadsupport is formed in the structure.
 15. The apparatus of claim 13,wherein: the minimum gap corresponds to an approximate 20% squeezereduction of the wall thickness of the one of the pair of tubing linesminus a maximum in-service deflection of the pre-loaded flexure; and themaximum in-service deflection and a spring constant of the pre-loadedflexure provide a pinching force on the one of the pair of tubing lines,when the pinching member is in the first position, of greater thanapproximately 45 pounds that varies within approximately 15% of nominalover the range of the maximum in-service deflection.
 16. The apparatusof claim 10, wherein the pinching member is rotatably mounted about anauxiliary axis that is offset from the central axis of the shaft. 17.The apparatus of claim 10, wherein each anvil has a radius betweenapproximately 0.06 inch (1.5 mm) and approximately 0.08 inch (2 mm). 18.A medical injection system comprising a pump having an inlet port and anoutlet port; a first tubing line including a first end coupled to theoutlet port of the pump and a second end adapted for connection to apatient line for injection of fluid from the pump; a second tubing lineincluding a first end coupled to the inlet port of the pump and a secondend adapted for connection to a fluid reservoir for filling the pumpwith the fluid; and a valve apparatus for controlling flow into and outfrom the pump, the valve apparatus comprising: a rotatable shaft; apinching member coupled to the rotatable shaft such that the pinchingmember moves around a central axis of the shaft when the shaft isrotated; a first anvil attached to a first spring member and located ona first side of the shaft; and a second anvil attached to a secondspring member and located on a second side of the shaft, the second sidebeing generally opposite the first side; wherein the first tubing lineis positioned between the pinching member and the first anvil of thevalve apparatus; the second tubing line is positioned between thepinching member and the second anvil of the valve apparatus; rotation ofthe shaft moves the pinching member from a first position to a secondposition; the pinching member compresses the first tubing line againstthe first anvil at the first position; and the pinching membercompresses the second tubing line against the second anvil at the secondposition.
 19. The system of claim 18, wherein each of the first andsecond spring members of the valve apparatus comprises an elongateflexure, each flexure having a fixed first end and a floating secondend, each second end having the corresponding anvil attached thereto.20. The system of claim 19, wherein the valve apparatus furthercomprises a pair of pre-load supports, each pre-load support beinglocated adjacent a corresponding floating second end of thecorresponding flexure for pre-loading thereof.
 21. The system of claim20, wherein the valve apparatus further comprises a fixed structuresupporting the shaft, the first fixed end of each flexure being coupledto the structure, and each pre-load support being formed in thestructure.
 22. The system of claim 20, wherein: a minimum gap betweeneach anvil and the pinching member in the corresponding positioncorresponds to an approximate 20% squeeze reduction of a wall thicknessof the corresponding tubing line minus a maximum in-service deflectionof each pre-loaded flexure; and the maximum in-service deflection and aspring constant of each pre-loaded flexure provide a pinching force oneach tubing line being compressed between the pinching member and thecorresponding spring-loaded anvil of greater than approximately 45pounds that varies within approximately 15% of nominal over the range ofthe maximum in-service deflection.
 23. The system of claim 18, whereinthe pinching member of the valve apparatus is rotatably mounted about anauxiliary axis that is offset from the central axis of the shaft. 24.The system of claim 18, wherein each anvil of the valve apparatus has aradius between approximately 0.06 inch (1.5 mm) and approximately 0.08inch (2 mm).
 25. A method for controlling flow through a tubing line ina medical injection system, the method comprising: positioning thetubing line between a pinching member and a spring-loaded anvil; andmoving the pinching member from a neutral position to a pinchingposition, at which the member compresses the tubing line against thespring-loaded anvil.
 26. The method of claim 25, wherein moving thepinching member comprises rotating a shaft to which the pinching memberis coupled so that the pinching member moves around a central axis ofthe shaft.
 27. The method of claim 25, wherein the pinching member isrotatable about an auxiliary axis that is offset from the central axisof the shaft, such that the pinching member rolls into contact with thetubing line, when the pinching member is moved to the pinching position.28. The method of claim 25, further comprising pre-loading a springmember of the spring-loaded anvil prior to moving the pinching memberfrom the neutral position.
 29. The method of claim 28, furthercomprising: establishing a minimum gap between the spring-loaded anviland the pinching member in the pinching position for an approximate 20%squeeze reduction of a wall thickness of the tubing line minus a maximumin-service deflection of the pre-loaded spring member; and wherein themaximum in-service deflection of the pre-loaded spring member provides apinching force on the tubing line being compressed between the pinchingmember and the corresponding spring-loaded anvil of greater thanapproximately 45 pounds, the pinching force varying within approximately15% of nominal over the range of the maximum in-service deflection. 30.A valve apparatus for controlling flow through a tubing line of amedical injection system, the apparatus comprising: a rotatable shaft; apinching member coupled to the rotatable shaft such that the pinchingmember moves around a central axis of the shaft when the shaft isrotated; and an anvil attached to a spring member and located alongsidethe shaft; wherein rotation of the shaft moves the pinching memberbetween a neutral position and a pinching position, the pinchingposition being adjacent to the anvil; and when the pinching member is inthe pinching position, a minimum gap between the anvil and the pinchingmember is less than twice a wall thickness of the tubing line.
 31. Theapparatus of claim 30, wherein the spring member comprises an elongateflexure having a fixed first end and a floating second end, the secondend having the corresponding anvil attached thereto.
 32. The apparatusof claim 31, further comprising a pre-load support located adjacent thefloating second end of the flexure for pre-loading thereof.
 33. Theapparatus of claim 32, further comprising a fixed structure supportingthe shaft; wherein the first fixed end of the flexure is coupled to thestructure and the pre-load support is formed in the structure.
 34. Theapparatus of claim 32, wherein the minimum gap corresponds to anapproximate 20% squeeze reduction of the wall thickness of the tubingline minus a maximum in-service deflection of the pre-loaded flexure;and the maximum in-service deflection and a spring constant of thepre-loaded flexure provide a pinching force on the tubing line, when thepinching member is in the pinching position, of greater thanapproximately 45 pounds that varies within approximately 15% of nominalover the range of the maximum in-service deflection.
 35. The apparatusof claim 30, wherein the pinching member is rotatably mounted about anauxiliary axis that is offset from the central axis of the shaft. 36.The apparatus of claim 30, wherein the anvil has a radius betweenapproximately 0.06 inch (1.5 mm) and approximately 0.08 inch (2 mm).